(1) Field of the Invention:
The present invention relates to dies for extruding honeycomb structures and a method of manufacturing said dies. More particularly, the invention relates to honeycomb structure forming dies which are adapted to form honeycomb structural bodies through extruding a plastic material such as a ceramic material and comprise a forming section provided with forming channels and made of a wear resistive alloy such as a super hard alloy, wherein a plurality of opening holes which communicate with the above forming channels and to which the plastic material is press fed are machined in the forming section through electrical discharging machining. The invention also relates to a method for manufacturing such dies.
(2) Related Art Statement:
As pointed out by the prior art in U.S. Pat. No. 3,790,654, there has been known a honeycomb forming die as shown in FIG. 1 (FIG. 1A is a plan view of the honeycomb forming die and FIG. 1B is a sectional side view of the die shown in FIG. 1A as viewed from an arrow (IB-IB). More particularly, the honeycomb structure forming die shown in FIGS. 1A and 1B is of a so-called integral structure, and is provided with honeycomb structure forming channels 3 (hereinafter referred to briefly as "forming channels") extending from a front face 1 of the die toward a rear face 2 thereof in a specified depth and in a sectional shape conforming to that of honeycomb structural bodies to be extruded (in the example shown in FIG. 1, a square shape). The die is also provided with a plurality of opening holes 4 which are independently bored from the die rear face 2 toward the die front face 1 and communicated with the forming channels 3. A raw material of the honeycomb structural bodies to be extruded, for instance, a ceramic plastic material is press fed to all the above plural opening holes 4, and the press fed plastic material flows into the forming channels 3 while being squeezed. Then, the plastic material is continuously extruded into ceramic honeycomb structural bodies through the forming channels 3.
However, when honeycomb structural bodies are extruded by using such a conventional honeycomb structural die, the forming channels 3 are worn with the plastic material passing through the forming channels 3, so that the width of the channels becomes larger. Thus, this poses a problem that expensive dies must be repeatedly exchanged so as to always assure a dimensional precision of the honeycomb structural bodies. In particular, when honeycomb structural bodies are to be formed through extrusion by using an alumina base material, a silicon carbide base material, a mullite base material, etc. having high hardness, the forming channels 3 are greatly worn. Therefore, there is an undesirable problem that the life of the die becomes conspicuously shorter.
Under the circumstances, in order to solve the above-mentioned undesirable problems, the prior art U.S. Pat. No. 4,653,996 discloses dies for extruding honeycomb structural body as shown in FIG. 2 in which a super hard alloy plate 5 is bonded to a front face of the die 1 and forming channels 3 are formed in the super hard alloy plate 5. However, in the die illustrated in FIG. 2, a part of the forming channels 3 extend inside a die base portion 6, and opening holes 4 are formed in the die base portion 6. Since the die base portion is not made of a super hard alloy, the opening holes 4 and a part of the forming channels 3 extending in the die base portion 6 more conspicuously wear as compared with the forming channels 3 formed in the super hard alloy plate 5. In particular, when a wear degree of a portion of the opening holes 4 near the forming channels 3 and a portion of the forming channels 3 in the die base portion 6 becomes non-uniform, a speed at which a plastic material passes through the forming channels 3 partially varies. Accordingly, there exists an undesirable problem that extruded honeycomb structural bodies are deformed or cracked during firing thus resulting in honeycomb structural bodies which are easily broken. Hence, even though the super alloy plate 5 is highly resistant to wear, the use life of the die depends upon wear of the die portion 6.